Prior valves, such as chokes, used to control high velocity flow which is damaging to the valve seat have utilized a replaceable valve seat insert including a blast tube which has generally been threaded into the body in the outlet. When such valves have been used they have been subject to wear and the valve seat insert is difficult to remove and replace since the hex head of the insert is subject to wear and may not be easily engaged and sometimes is extremely difficult to remove.
In one prior choke the bonnet is provided with a tubular projection extending into the body chamber and into the body outlet with the inlet extending into the tubular projection. Cam actuated pins are used to engage the tubular projection to retain the bonnet in the body. The valve member and seat include a pair of discs with openings therein which can register or be restricted by rotation of the valving disc. The seat disc rests on a shoulder positioned in the bore of the tubular member. Another prior choke is shown in European Petroleum Conference Paper EUR 370 "New Subsea Choke and Choke Calibration System" as presented at the European Petroleum Conference in London, England in October 1982. This choke uses locking dogs to engage the tubular projection to retain the bonnet in the body. This choke also uses a pair of discs which rotate relative to each other to open or restrict the flow area. Such structures do not include a tapered plug valve member and an annular valve seat, both of which are of a material which is resistant to the erosion of high velocity fluid flow and are removable as a unit.